Keith is not being disingenuous "D"....you are.
The slogan was "political speak", but it was not a lie.

If the slogan had said "we will spend that money on the NHS"...that would have been a lie, unless of course the government do spend it on the NHS, then it would be the truth.

"Let's spend the money on the NHS instead" is an invitation to consider how the money should be sensibly spent.